Solvent refining of mineral oil



Dec. 6, 1938. E. G. MCFARLAND SOLVENT REFINING OF MINERAL OIL Filed Nov. 24, 1936 Patented Dec. e, 193s PATENT OFFICE y SOLVENT REFINING OF MINERAL OIL Edward Gardner McFarland, Lawrenceville, Ill., assignor to The Indian Refining Company, Lawrenceville, Ill., a corporation of Maine Application November 24, 1936, Serial No. 112.475

8 Claims.

This invention relates to solvent refining of mineral oil, and more particularly to the recovery of the solvent from the refined oil for reuse in the process.

In the solvent refining of mineral oil, such as lubricating oil, with a selective solvent of the character of furfural, for example, it is customary to recover solvent from the refined oil by stripping with steam. When lubricating oil, which contains a small percentage of lighter oil fractions such as naphtha, is refined in this manner, the lighter oil or naphtha may be removed in whole or part during the steam stripping operation which is customarily employed to recover the last trace of retained solvent from the refined oil. In order to render such a solvent refining process economical and practical, it is essential that the solvent be recovered substantially completely for reuse so that the sol- Vent loss in the process is kept at a very small amount. The above mentioned steam stripping operation introduces water into the system, and this water must be separated from the solvent prior to reuse of the recovered solvent in subsequent reiining operations. This separation of water from the solvent is customarily accomplished by a series of stripping, fractionating and settling operations, so that the water content of the recovered solvent is reduced to a very small ligure of the order of less than 0.50%. When lighter oil fractions, such as naphtha, are present in the oil being refined, and these fractions removed in the stripping operation as above described, it is found that this lighter oil carries over into the fractionating and settling operations and interferes with them. Moreover, the accumulation of such lighter oil in the solvent system is objectionable as altering the composition of the solvent and interfering with the rening operations.

It is an object of the present invention to provide an improved method of recovering such a selective solvent substantially free from water and at the same time to remove any lighter oil from the solvent system in a simple and effective manner so that such lighter oil does not interfere with the recovery operations.

In accordance with the present invention, the refined oil containing a portion o'f solvent is treated to remove that solvent by distillation andy steam stripping. The mixture of water vapor, lighter oil vapor and solvent removed in the steam stripping operation is passed to a fractionating zone maintained at a temperature below the boiling point of water at the prevailing pressure where it condenses to form a lean mixture of primarily water containing a small proportion of the solvent and lighter oil. This mixture is stripped with steam and the vapors consisting of an enriched mixture of solvent and lighter oil with steam are passed to a fractionating zone maintained at a temperature to condense primarily solvent and allow steam and the lighter oil vapors to pass overhead. These overhead vapors are condensed and passed to a decanter where the condensate is allowed to stand and stratify into a light oil layer and a water layer containing dissolved solvent. The light oil is removed at this point from the solvent system and the water layer containing dissolved solvent is returned to the last mentioned fractionating zone to provide reflux therefor. Condensate from this fractionating zone is allowed to stratify into a water layer which is returned to the rst mentioned fractionating and steam stripping zone, and the enriched solvent layer is then passed to further settling and drying zones where the water content is reduced to the desired lowgpercentage.

In the drawing, the single figure is a diagrammatic View of a preferred embodiment of apparatus for carrying out the method of this invention. Referring to this drawing, the oil to be reiined is charged through the line III by pump I I and passed through a suitable steam heater I2 where it is indirectly heated by steam to the desired refining temperature. -By way of example, this invention is hereinafter described in connection with the refining of a Mid-Continent distillate lubricating oil with furfural, although it is to be understood that the invention can be employed in the rening of other types of distillate and residual oils with any of the selective solvents of the character of furfural, nitrobenzene, phenol, and the like, which are customarily employed. The heated oil at a temperature of the order of 200 F. is introduced by line I3 into the lower portion of the counterflow treating tower I4 shown as containing four layers of raschig ring packing I5.

Furfural is simultaneouslyipumped from storage tank I6 by pump I1 through steam heater I8 and. a refined oil heat exchanger I9, and then introduced at a temperature of the order of 240 F. by line 20 into the upper portion of tower I4. The ratio of solvent to oil is preferably of the order of 2:1 up to 3:1. The oil rises through the solvent, which latter gravitates towards the bottom of the tower. The furfural is selective as between paralnic and to solvent recovery through the line 2|.

The refined oil mix is withdrawn from tank 23 by pump 24 and forced through a heating coil 28 in the convection bank of a pipe still heater 28. The mix at a temperature of about 270 F. is delivered by line 21 into the upper portion of a reilned oil stripping tower 28 provided with an upper series of bubble trays 28 and a lower series oi' inclined contact trays 38. Oil accumulating in the bottom of the tower is recirculated by pump 3|, through line I2 and heating coil 83 in the radiant section of furnace 28 and thence passes at a temperature oi'- about 460 F. by line 84 into an intermediate portion of tower 28 above the inclined contact ltrays 80. 'I'his supplies the mainheating of tower 28, which may be operated at a bottom temperature of around 425 F. and a top temperature of around 220 F. and under a vacuum equivalent to an absolute pressure of about 2" of mercury. At these temperatures and with the vacuum maintained therein, most of the furiuraljs driven of! from the rened oil and is drawn as vapor through vapor line to a solvent condenser 38 and then by line 31 into a solvent accumulator drum 88. Vacuum on the system is maintained by dry vacuum pump 39 communicating with the upper portion of solvent drum 38 through vapor line 40.

A small proportion of the solvent is still retained in the oil. This is removed by passing a portion of the oil recirculated by pump 3l through a branch line 4I discharging into the upper portion of a refined oil steam stripper 4| containing bubble trays 48. The amount of oil passed to the stripper 42 is controlled by a oat mechanism 44 responsive to the oil level in tower 28. The iloat mechanism regulates a valve 45 in line 4I to maintain a normal liquid-level in tower 28. Stripper 42 may operate at substantially atmospheric pressure with a bottom temperature oi' around 385 F. and a top temperature of around 175 F. Steam is directly injected into the bottom of stripper 42 by line 48 and serves to strip out remaining traces of solvent and lighter oil vapors from refined lubricating oil. The reiined oil is discharged from the base of stripper 42 through line 41, and forced by pump 48 through line 48, reiined oil heat exchanger I8, line 50, retlned oil cooler 5| and line 52 to storage.

As the solvent is an expensive item oi' the process it is highly desirable to cut down solvent loss to a minimum. Moreover, as the presence of water above a certain maximum content of about 0.50% in the solvent is objectionable when that solvent is reused for further rening operations. the stripped vapors from stripper 42 are further processed to separate the solvent from the water and to also remove any lighter oil which may be present. As shown, the vapors are passed by vaporline 84 into an intermediate portion of a solvent stripper 55 below a trap tray 88. 'Ihis tray 88 divides the tower into a lower fractionating zone containing bubble trays 81 and an upper i'ractionating zone containing bubble trays 88. The temperature within the solvent stripper is maintained below the boiling point of water at the prevailing atmospheric pressure so as to condense water vapor in the lower 'iractionating section 81. This condensate which will also contain a small proportion oi' furfural and light oil passes downwardly from tray to tray in the lower stripping section 81 countercurrent to a rising current of steam introduced by line 59 which serves to sweep out remaining traces of solvent and lighter oil from the water. The steam serves to carry the solvent and lighter oil in vapor form above the trap tray 88 through the center vapor dome thereof and into the upper fractionating section 58. Condensed water substantially devoid oi solvent collecting in the base of stripper 55 is discharged by line 88.

'I'he vapors thus introduced into the upper fractionating section 58 consist of an enriched mixture oi furfural and steam with any lighter oil vapor which may .be present. Adequate refiuxing is provided for this upper iractionating section of the stripper in order to condense primarily furfural therein. The temperature of this section of the tower is regulated by the supply oi reilux so that mainly the highest boiling constituent, namely the furfural, is condensed as the vapors are fractionated therein, while a lean mixture of primarily steam with some furfural vapor and any light oil vapor passes overhead by vapor line 8i to a condenser 82. The condensate flows into adecanter 83 where it is allowed to stand and stratify into a lower water layer containing dissolved furfural and an upper light oil or naphtha layer. The light oil layer is discharged from the upper portion of decanter 63 through line 84 and is thus removed from the system. The lower water layer is returned from the lower portion of decanter 83 through line '85 into the upper portion of solvent stripper 55 above trays 58 to supply reflux for this upper fractionating section. In explanation, it may be pointed out that the vapors passing overhead through line 8| consist mainly of steam with only a small proportion of furfural. Under these conditions, the furfural in the condensate passed to decanter 88 is dissolved substantially completely in the water layer, while the condensed lighter oil or naphtha will be substantially immiscible with this water layer and thus can be removed without appreciable loss of solvent.

The condensate from the upper stripping section 58 of solvent stripper 58 accumulates on trap tray 58 and there straties into an upper water layer containing only a small proportion of dissolved furfural and a lower furfural layer containing only a small proportion of. water. 'I'he upper water layer is allowed to overilow through the dome of the trap tray and thus be returned to the lower stripping section 51 as reflux, and the small proportion of furfural dissolved in this water so returned is then stripped out by steam introduced at 58 so that this solvent is eventually recovered. The lower furfural layer is continuously discharged by line 88 and passed through a solvent cooler 81 into an accumulator drum 88. It is here allowed to stand and further stratiiy into an upper water layer containing a small proportion of dissolved furfural and a lower furfural layer containing a very small proportion of dissolved water. The upper water layer which is comparatively rich in furfural is returned by line 88 to the upper fractionating section I8 oi' solvent stripper 8l to be reprocessed and to furnish additional reiiux. The lower iurfural layer is passed i'rom accumulator drum 88 through line into a dryer 1| where it is indiabove the boiling point of water to vvaporize remaining traces of water in the solvent. This vapor is removed by vapor line 12 to a condenser 13, and the condensate then returned by pump' 14 and line 15 to the upper fractionatlng section 58 of solvent stripper 55 for reprocessing and to provide additional reflux.

The dried solvent is discharged by line 18 through solventl cooler 11 into a sample accumulator drum 18. The latter is equipped to remove samples at regular intervals to see that the solvent is on test and that the water content is below the maximum allowable. If it is on test, it is passed by line 19 to the solvent accumulator drum 38 where it is added to the solvent recovered in the refined oil stripping tower 28. Recovered solvent overflows from accumulator drum 38 into an overflow drum 80, from the bottom of which it is withdrawn by pump 8| and forced through line 82 to the solvent storage tank i6 for reuse in the process. Makeup solvent may be added as needed to tank i6 by line 83 to compensate for solvent loss.

In order to recover any uncondensed solvent vapors withdrawn from the accumulator drum 38 through vapor line 40 by the vacuum pump 39, the discharge from the vacuum pump is forced by vapor line 84 through an after-cooler 85 into a solvent drip drum 86 where condensed solvent drops out of the vapors. This solvent is passed by line 81 into a slop solvent tank 88. Uncondensed vapors are removed from drum 86 by vapor line 88 opening into the upper portion vent 90. This recovered solvent is returned from.

tank 88 by pump 9| through line 82 to the upper portion of the lower fractionating section 51 of solvent stripper 55 for reprocessing. In case the solvent in sample accumulator drum 18 is not on test, it may be passed by line 83 into the slop solvent tank 88 from where it is returned by pump 9| and line 92 to the solvent stripper 55 for reprocessing.

In this manner, the solvent is effectively recovered from the refining operation, while at the same time water and light oil are continuously removed from the system. The solvent loss is therefore reduced to about 0.02% or less of the solvent handled. While the invention has been described by way of example in connection with the recovery of solvent from the ramnate or rened oil from counterfiow tower I4, it is to be understood that the invention is applicable to the recovery of solvent in a similar manner from the extract mix discharged by line 2l. 'I'his extract mix may be passed through a heater and then to an extract stripping tower and finally to an extract steam stripper in the manner described above in connection with the recovery of solvent from the raffinate. The dry solvent removed by the extract stripping tower may be passed through a condenser and then into the solvent accumulator drum 38. 'Ihe Wet solvent recovered by the extract steam stripper may be passed by a vapor line to the solvent stripper 55 for processing in the manner described above, so that the solvent stripper and related apparatus for drying of the solvent is common to the processing of wet solvent recovered from both the rafnate and the extract. As this apparatus is substantially identical with that shown for the recovery of solvent from the reiined oil, further illustration thereof is thought unnecessary and it has purposely been omitted to avoid duplication and effect simplication of the drawing. Wherever the expression solvent recovered from the refined oil" is employed, throughout the description and claims, it is ,to be understood that this refers to the recovery of solvent from the so-called extract as well as from the so-called ramnate. While the invention has been speciflcally described in connection with the use of furfural as the refining solvent, it is to be understood that the invention is also applicable to the recovery of other solvents customarily used in the solvent refining of mineral oil and which are selective as between paraftlnic and nonparafnic constituents of the oil.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In the solvent refining of heavier mineral lubricating oil containing some lighter oil with a solvent which is partially miscible with water and which is highly selective between paraiiinic and non-paraffinic hydrocarbons, and wherein the solvent is recovered from the refined oil by steam stripping to produce a lean water mixture containing solvent and lighter oil, the method in the separation of the solvent from the water and lighter oil of said mixture which comprises stripping the solvent and lighter oil with steam from said lean mixture of the same in water in a stripping zone, passing the stripped vapors enriched in solvent to a fractionating zone and condensing solvent therein, removing a lean` mixture of uncondensed vapors consisting primarily of water together with some solvent and lighter oil vapors from the fractionating zone and condensing them, passing the condensed lean mixture to a settling zone where the condensate stratifies into a water slayer containing solvent dissolved therein and a. lighter oil layer, removingthe lighter oil layer, returning the water layer containing dissolved solvent as reux to the fractionating zone, separating a water layer from the condensed solvent layer in the fractionatlng zone and returning the water layer to the stripping zone, removing condensed solvent from the fractionating zone, and removing water substantially free from solvent from the lower portion of the stripping zone.

2. The method of claim 1, wherein condensed solvent from the fractionating zone is passed to an accumulating zone where it is allowed to settle and stratify into an enriched solvent layer and a lean water layer, and the water layer is returned to the fractionating zone to provide additional reux.

3. 'I'he method of claim 1, wherein condensed solvent from the fractionating zone is passed to an accumulating zone where it is allowed to settle and stratify into an enriched solvent layer and a lean water layer, the water layer is returned to the fractionating zone to provide additional reiux, the enriched solvent layer is passed to a drying zone where it is heated to drive off retained water inthe form of steam mixed with some solvent vapor, and the vapors from the drying zone are condensed and the condensate returned to the fractionating zone for reprocessing.

4. The method of 1 wherein the temperature of the i'ractionating zone isrcontrolled to condense primarily 'solvent therein and to allow water vapor and lighter oil vapor mixed with some solvent vapor to pass overhead and be removed from the fractionating zone for condensation into a lean water mixture with which the lighter oil is substantially immiscible so that it will stratify as a. separate layer while the solvent will be substantially competely dissoved in the lcondensed water.

5. In the solvent rening of mineral lubrieating oil containing some lighter oil with furi'ural, and wherein Iurfural is recovered from the rened oil by steam stripping to produce a lean water mixture containing furfux'al and lighter oil,

the method in the separation of furiural from water and lighter oil of the said mixture which comprises stripping the furfural and lighter oil with steam from said lean mixture of the same in water in a stripping zone, passing the stripped vapors to a fractionatlng zone and condensing turfural therein, removing a lean'mixture of vapors consisting primarily of water vapor containing lighter oil vapor and a small proportion otiuriural vapor from the iractionating zone and condensing them, passing the condensate to a settling zone to stratify into an upper lighter oil layer and a lower water layer containing -i'urfural dissolved therein, removing the lighter oil layer, returning the water layer containing dissolved iurfural as reflux to the fractionating zone, separating a water layer from the condensed Iuriural layer inthe fractionating zone and returning the water layer to the stripping zone, removing condensed furfural from the fractially i'ree from i'urtural from the lower portion of the stripping zone.

6. The method of claim 5, wherein condensed furtural from the iractionating zone is passed to an accumulating zone where it is allowed to settle and stratiiy into a lower enriched furtural layer and an upper water layer containing a small proportion ot dissolved furfural, and the upper water layer is returned to the fractionating zone to provide additional redux.

7. The method of claim 5, wherein the condensed furrurul from the fractionatlng zone is pasd to an accumulating zone where it is allowed to settle and stratify into a lower enriched i'urfural layer and an upper water layer containing a small proportion of dissolved furtural, the

tionating sone, and removing water mbstan vwater layer is returned to the iractionating zone to provide additional reiiux, the enriched furfural layer is paed to a drying zone where it is heated to drive on' retained water as steam mixed with some furtural vapor, and the mixed vapors from the drying zone are condensed and the condensate returned to the iractionating zone for reprocessing.

8. The method of claim 5, wherein the furi'ural and lighter oil are stripped with steam from the lean mixture at a temperature below the boiling point of water at the prevailing pressure, and wherein the temperature of the fractionating zone is controlled to condense primarily furfural therein and to allow water vapor and lighter oil vapor mixed with a small proportion of furfural vapor to pass overhead and be removed from the fractionating zone before condensation thereof.

' EDWARD GARDNER MCFARLAND. 

